package org.example.les01;

import java.io.IOException;
import java.net.BindException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;
import java.nio.charset.StandardCharsets;

/**
 * 基于UDP的回显服务器
 */
public class Demo01_UDPEchoServer {
    //声明一个提供UDP服务的对象
    private DatagramSocket socket;
    //通过构造方法指定服务器的端口号
    public Demo01_UDPEchoServer(int port) throws SocketException {
        //校验端口号
        if(port<1024||port>65535){
            throw new BindException("端口号必须在1024和65535之间.");
        }
        //初始化UDP服务端对象
        this.socket=new DatagramSocket(port);
    }

    /**
     * 处理用户请求
     */
    public void start() throws IOException {
        System.out.println("服务器已启动.");
        //循环处理用户请求
        while(true){
            //1.使用DatagramPacket来接收用户发来的数据
            DatagramPacket requestPacket=new DatagramPacket(new byte[1024],1024);
            //2.接收数据
            socket.receive(requestPacket);
            //3.解析接收到的数据
            String request = new String(requestPacket.getData(), 0, requestPacket.getLength(), "UTF-8");
            //4.通过请求计算响应
            String response=process(request);
            //5.使用DatagramPacket封装响应的数据
            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(StandardCharsets.UTF_8), 0, response.getBytes().length, requestPacket.getSocketAddress());
            //6.发送响应
            socket.send(responsePacket);
            //7.打印日志
            System.out.printf("[%s:%d] request=%s, response=%s\n",requestPacket.getAddress().toString(),requestPacket.getPort(),request,response);

        }
    }

    /**
     * 计算响应的方法
     * @param request
     * @return
     */
    protected String process(String request) {
        return request;
    }

    public static void main(String[] args) throws IOException {
        Demo01_UDPEchoServer server = new Demo01_UDPEchoServer(8888);
        server.start();
    }
}
